Very recently acquired by Red Hat, Gluster offers open source file systems for public and private cloud-based storage. Used with commodity hardware, the Gluster file system can create network storage solutions that scale out to 72 brontobytes. (The number of bytes in a brontobyte is a one followed by 27 zeros.) Operating System: Linux

Virtualization

Used by many commercial cloud services, the Xen hypervisor is included in most Linux distributions and is also available as an appliance. Many commercial virtualization products, including the Citrix XenServer, are built on top of Xen. Operating System: Windows, Linux, Solaris, others

OpenVZ takes a different approach to virtualization: unlike VMware, VirtualBox and many other virtualization solutions which use VMs, OpenVZ offers container-based virtualization through VEs or VPSs. Commercial products based on OpenVZ are sold as Parallels Virtuozzo Containers. Operating System: Linux

Short for "Kernel-based Virtual Machine," KVM allows users to run multiple Linux or Windows virtual machines on a single server. Like Xen, it's included in many Linux distributions. Operating System: Windows, Linux

Web Servers

Used by 63 percent of all websites, Apache has been the most popular Web server for more than a decade. It prides itself on being secure, efficient and extensible. Operating System: Windows, Linux, OS X

Nginx (pronounced "engine X") is both an HTTP and a mail proxy server. Currently powering about 8 percent of all websites, it's the third most popular Web server. Operating System: Windows, Linux, OS X

Most of them time when you want to install the Apache Web server, you'll also need other tools, like MySQL, PHP and Perl. This group of downloads bundles together all of those tools—along with a variety of other open source software that's helpful for running a Web server—in an easy-to-deploy package customized for each of the major operating systems. Operating System: Windows, Linux, OS X, Solaris

The goal of the App Serv project is simple: allow users to set up a Web server with Apache, MySQL and PHP in one minute or less. Note that this project originated in Thailand so some of the English documentation reads a little strange. Operating System: Windows, Linux

Wiki/Collaboration

If you just need a simple wiki, DokuWiki is easy-to-use, standards compliant and doesn't require a separate database. Commercial support is available through a variety of third-party companies. Operating System: OS Independent

Best known as Wikipedia's software, MediaWiki can handle extremely large projects with terabytes of data and thousands of hits per second. It's extremely customizable and is fairly simple for end users to learn. Operating System: Windows, Linux/Unix, OS X

Althought it's a little tough to find the open source version of MindTouch on the company's website, the source code for the core wiki program is still available for a free download. According to the website, it's been ranked the number one open source collaboration tool. The company offers several other products based on the open source engine. Operating System: Windows, Linux

More than just a wiki, TikiWiki also offers support for forums, blogs, image galleries, map servers, RSS feeds, bug trackers and more. It has been downloaded more than 900,000 times and currently powers tens of thousands of websites. Operating System: OS Independent

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